Electrodynamic sound reproducing system



Dec. 1, 1931. L, J BOBB 1,834,820

ELECTRODYNAMIC SOUND REPRODUCING SYSTEMl Filed Jan. 22, 1930 Away 25W wa /aim Patented Dec. 1, 193T UNIA'TED- STATES'PATENT OFFICE LLOYD J. 30183, 01 PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO- PHILADELPHIA STORAGE BATTERY COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORA- TION or PENNSYLVANIA ELECTRODYNAMIO SOUND REPRODUCING- SYSTEM Application filed January 22, 1930. Serial No. 422,638.

The present invention relates to sound re-.

producing systems and particularly refers to systems employing sound reproducing devices known-in the art as electrodynamic re- !5 producers which have a movable coil armature adapted to vibrate in accordance with signal currents flowing therein and a fixed field coi-l adapted to be energized from an external source. l0 The principal object of the invention is to provide means for energizing the fixed field coil of the sound reproducer from a source of pulsating uni-directional current such as rectified alternating current of 60 cycles andllO volts, although other he quencies and voltages may be used without materially affecting the operation; or from any other source of pulsating uni-directional current such as adynamo-electric machine ,Whichmay generate a uni-directional current having a commutator ripple. "Another object is to provide means to substantially reducingrthe hum effects which are generally present in rectified alternating 2 current supply systems and which cause annoying disturbances in the sound reproducer or loud speaker. A further object is to provide energization of the fixed field coil of the sound re- 3e producer from the filter system of a rectified alternating current supply as is generally used for energizing vacuum tubes of aradio. signaling system. Other objects and'advantages of the invention will appear more fully hereinafter from the following detailed description taken together with the accompanying drawings;

in which: I

Fig. 1 is a schematic diagram of an electrodynamic sound-reproducer connected in accordance with my invent-ion;

Fig. 2 is' a further modification. showing the sound reproducer energized from the filter system of a power supply of a vacuum tube signaling system.

Referringto Fig. '1 of the drawings, the sound reproducer comprises the usual fixed field coil L, the movable-armature coil L associated therewith and the vibrating diaphragm LS, which may be a cone or any other acoustic diaphragm and which may be attached to the'vibrating coil in any suitable manner. The field coil L is energized from an alternating current source through a suitable transformer T through the rectifier D which may be a half-wave 01' a full-wave rectifier of any suitable t pe such as an electrolytic rectifier, a metal ic rectifier of the dry type or a thermionic tube rectifier. The armature coil L is adapted to be energized by signaling currents from the transformer T which may be, in the present instance, the output transformer of the last stage of amplification of a receiving system which may be of the push-pull type. The signal currents flowing through the coil L react on the field produced by the coil L and cause the armature coil L to vibrate in accordance with the signal currents, thereby vibrating the diaphrgm LS to generate sound. The

current flowing through the field coil L fluctuates more or less due to the inherent action of the rectifier D thereby producing a fluctuating field which affects the vibrating'coil L and these fluctuations are reproduced in the diaphragm LS in the form of a steady audible hum which is annoying and nude sirable in sound reproduction. To eliminate this undeslrable hum or to atleast reduce it to a substantial minimum, a resistance R is provided in shunt with the field coil L to in- I troduce 'a desired portion of the fluctuating current into the armature coilL in opposition to the fluctuations produced therein by the action of the fluctuating field. The fluctuations introduced into the coil L by means of the resistance R and those which are present in the coil L due to the acttion of the fluctuating field being of the same general character but arranged in opposite phase by means of the resistance R, they substantially neutralize. each other, thereby eliminating undesirable hum in the sound reproducer LS.

The amount of the fluctuating current de- .sired to be introduced into the coil L may be determined by meansof the variable ta P which may be permanently set after the desired adjustment is found.

In F i 2 is shown an arran ement in which a source of signal currents whereby said mov used additionally as a choke coil of a filter system of the general type which includes the condensers C and 0 connected across the output of a thermionic tube rectifier D, the plates of which are energized from the secondary S and the filament from the secondary S1 of the transformer T which is connected' to an alternating current supply by means of the primary P The output of the rectifier is connected through the filter to a load indicated at Z which may be the plate circuits of a'cascaded series of vacuum tubes of a radio signaling system. As shown in Figs. 1 and 2, the armature coil L is energized with signaling currents from the transformer T and the opposing fluctuations are introducedinto the armature coil L by means of the resistance R connected in shunt with the field coil L and the amount of the fluctuating current may be varied by the variable tap P as before. The function of the circuit of Fig. 3 is similar to that of Fig. 1 except that the field coil L performs an additional function of a filter choke, thereby eliminating the use of a separate choke coil. It is obvious that the opposing fluctuation-s may be introduced into the armature coil L by other means than the resistance R.

All of the modifications described may, of

course, be used to function in a manner re-' verse to that'described, that is, instead of" being used for sound reproduction, they may be used as a sound pick-up and the diaphragm LS may be replaced by a microphone diaphragm, in which case, sound vibrations cause the movable coil L to vibrate and gen- 1. In a device for translating electrical sig nal energy into sound energy having a fixed coil,.a movable coil associated with said fixed coil and adapted to be vibrated in the field of said-fixed coil, means for energizing said fixed coil from a source of pulsating uni-di-- rectional current whereby undesirable fluctuations are produced in sa1d movable-coil, means for energizing said movable coil from able 'coil is caused to vibrate in accordance with said s1gnal currents, and means connected 1n shunt with said fixed 0011 for introducing fluctuations into said movable coil.

which are substantially equal and opposite in phase'to the, undesirable fluctuations prowhereby said undesirable fluctuations are substantially neutralized and their effects on said device largely eliminated.

2. In a device for translating electrical signal energy into sound energy having a'fixed coil, a movable coil associated with said fixed coil and adapted to be vibrated in the field of said fixed coil, means for energizing said fixed coil from a source of pulsating uni-directional current whereby undesirable fluctuations are produced in said movable coil, means for actuating said movable coil from a source of signal currents whereby said movable coil is caused to vibrate in accordance with said signal currents, and means con nected in parallel with said fixed coil and having at least a portion thereof connected in series with said movable coil for introducing fluctuations into said movable coil which are substantially equal and opposite to the undesirable fluctuations produced in said movable coil by said fixed coil whereby said undesirable fluctuations are substantially neutralized and their effects on said device largely eliminated. p 1

3. In a device for translating signal energy into sound energy, the combination of I a source of alternating current, a rectifier for converting said alternating current into uni-directional current having a ripple component, a coil connected between the electrodes of said rectifier whereby a strong magnetic field of constant polarity is developed around said coil, a conductive element mounted for vibrational movement Lwithin said field, means for passing signal currents through said conductive element, whereby said conductive element is vibrated at the signal current frequency, and means connected in parallel with said coil for diverting and introducing a regulable portion of said ripple component of said uni-directional current from said 'coil into said conductive element of a phase to substantially eliminate vibration of said conductive member by the variation in field intensity caused by the ripple component of said uni-directional current.

LLOYD BOBB. 

